The present invention relates to a process for gettering semiconductor devices, particularly silicon semiconductor devices and to the semiconductor devices obtained from this process.
In the semiconductor art, gettering is understood to mean the subsequent removal of interfering impurities from semifinished or finished semiconductor devices.
Known gettering methods for devices based on crystalline silicon are, for example, the application of P.sub.2 O.sub.5, B.sub.2 O.sub.3 and similar glass oxides to the active region of the device, producing greatly disturbed surfaces on the rear of the device, e.g. by ion bombardment or mechanical roughing, providing nitride layers on the rear of the device or high temperature tempering in a nitrogen atmosphere. The gettering has the effect that in the active zone of the device interfering foreign atoms, particularly heavy metals, diffuse preferably into the getter layer, which is then removed so that less impurities remain in the device. Crystal defects are electronically inactivated by diffusing out silicon atoms and/or foreign atoms and subsequent rearrangement of the silicon crystal lattice. Usually, the gettering process is a combination of these two procedures.
In addition to having a number of advantages, the known gettering methods also have several considerable drawbacks. For example, in the first-mentioned method, (applying P.sub.2 O.sub.5, B.sub.2 O.sub.3 and similar glass oxides to the active region of the device), although the getter layer acts directly on the active zone of the device and permits the realization of a high gettering effect with a short gettering time of about one hour, these getter materials discharge undesirable impurities to the silicon layer. Moreover, this getter layer can sometimes be removed only with difficulty. Although with the creation of greatly disturbed surfaces on the rear of the device, the electronic properties are not influenced, because no foreign atoms are present, and the getter layer can be removed again with ease, the gettering in this process is effected from the rear of the device through the entire base material. To therefore improve the active layer, long gettering times are required (6 to 24 hours). The application of nitride layers to the rear of the device has the advantage of less influence of nitrogen as an impurity, but has the same drawback as the process described above, particularly the long gettering times. With high temperature tempering of the silicon semiconductor device in a nitrogen atmosphere, the small influence of nitrogen as an impurity is an advantage, but long gettering times and high temperatures are again required because the surrounding gas atmosphere acts as a low density getter.
Thus all previously known gettering methods have considerable deficiencies, such as the discharge of interfering impurities into the active region of the device and long gettering times at increased temperature which cause doping profiles in the device to shift and thus make it unusable.